It is common for a work machine such as but not limited to hydraulic excavators, wheel loaders, loading shovels, backhoe shovels, mining equipment, industrial machinery and the like, to have one or more actuated components such as lifting and/or tilting arms, booms, buckets, steering and turning functions, traveling means, etc. Commonly, in such machines, a prime mover drives a hydraulic pump for providing fluid to the actuators. Open-center or closed-center valves control the flow of fluid to the actuators.
Some modern machines have replaced the traditional hydraulic system described above with an electro-hydrostatic actuator system (EHA). An electro-hydrostatic actuator includes a reversible, variable speed electric motor that is connected to a hydraulic pump, generally fixed displacement, for providing fluid to an actuator for controlling motion of the actuator. The speed and direction of the electric motor controls the flow of fluid to the actuator. Power for the electric motor is received from a power unit, for example a generator, a power storage unit, such as a battery, or both. A system that includes an electro-hydrostatic actuator is referred to herein as an electro-hydrostatic actuator system. At, for example, deceleration and/or lowering motion of a load, the power unit receives power from the said electric motor that is then operated as a generator.